It may be useful, in a variety of settings, to utilize both a traditional engine (e.g., an internal combustion engine) and an infinitely variable power source (e.g., an electric or hydrostatic motor, a variable chain drive, and so on) to provide useful power. For example, a portion of engine power may be diverted to drive a first infinitely variable machine (e.g., a first electric machine acting as a generator), which may in turn drive a second infinitely variable machine (e.g., a second electric machine acting as a motor using electrical power from the first electrical machine). In certain configurations, power from both of types of sources (i.e., an engine and an infinitely variable power source) may be combined for final power delivery (e.g., to a vehicle axle) via an infinitely variable transmission (“IVT”) or continuously variable transmission (“CVT”). This may be referred to as “split-mode” or “split-path mode” operation because power transmission may be split between the mechanical path from the engine and the infinitely variable path. Split-mode operation may be attained in various known ways. For example, a planetary gear set may be utilized to sum rotational power from an engine and from an electric machine, with the summed power transmitted downstream within an associated power train. This may allow for delivery of power (e.g., to vehicle wheels) with an infinitely variable effective gear ratio. Various issues may arise, however, including limitations relating to the maximum practical speed of variable power sources.